This invention relates generally to the implantable medical devices and more specifically to telemetry systems for allowing communication between implanted medical devices and external programmers or monitors.
In the context of implantable medical devices, it has become common to provide a communication link between the implanted device and an external programmer or monitor in order to allow for transmission of commands from the external device to the implanted device and to allow for transmission of stored information and/or sensed physiological parameters from the implanted device to the external programmer. Conventionally, communication between an implanted device and an external programmer has been accomplished by means of a telemetry system which includes a transceiver located within the implanted medical device and an external programmer or monitor, each having a radio transmitter/receiver and one or more antennas.
The implanted device typically includes an antenna located either within the hermetic device housing containing the circuitry, as disclosed in U.S. Pat. No. 4,542,532 issued to McQuilkin, in a plastic header or connector block used to interconnect the device to electrical leads as disclosed in U.S. Pat. No. 5,697,958 issued to Patrick et al. or mounted to the device housing as in U.S. Pat. No. 5,861,019 issued to Sun et al. and U.S. Pat. No. 5,720,770 issued to Nappholz et al., all incorporated herein in their entireties. The programmer or monitor typically includes or consists of a programming head containing an antenna, intended to be placed on the patient""s body in close proximity to the implanted device. The programming head may be coupled to the external programmer or monitor by means of a cord, as disclosed in U.S. Pat. No. 5.766,232 issued to Grevious et al.
More recently it has been proposed to provide communication systems for implantable devices in which the programming head is done away with, and communication occurs directly between the programmer or monitor, which may be located some distance from the patient, and the implanted medical device. Such systems are disclosed in U.S. Pat. No. 5,404,877 issued to Nolan et al, and U.S. Pat. No. 5,113,869 issued to Nappholz. In the Nappholz patent, in particular, the use of an electrical lead as the antenna for broadcasting RF signals to the programmer or monitor which may be located some feet away from the patient is suggested.
The present invention is directed toward a telemetry system for an implantable device which, like the devices in the above cited Sun et al., Patrick et al., Nolan and Nappholz patents in which the antenna is located external to the hermetic housing of the implantable device.
The antenna of the implanted device may take the form of a monopole antenna located external to the hermetic enclosure of the implanted device, having a length tuned to function optimally at the radio frequencies chosen for use in the telemetry system. The antenna itself may, for example, correspond to any of the implantable device antennas illustrated in commonly assigned co-pending U.S. patent application Ser. No. 09/302,932, filed Apr. 30, 1999 by Villaseca et al. for a xe2x80x9cTelemetry System for Implantable Medical Devicesxe2x80x9d, incorporated herein by reference in its entirety. Alternatively, the antenna may correspond to any of the antennas described in the above-cited Sun et a., Nappholz, Nolan or Patrick et al. patents cited above.
Implantable stimulators or monitors employing electrodes or other sensors and employing antennas located external to the device housing have typically required a separate feedthrough to connect the antenna to the transceiver within the device housing, in addition to one or more feedthroughs to connect electrodes or sensors to the pulse generators and/or sensing circuitry within the device housing. The inventors of the present invention have developed a telemetry system in which the transceiver can share a feedthrough with a sensor or a stimulation or sensing electrode, reducing the total number of feedthroughs required for the device. In particular, the present invention provides a diplexer which separates the higher frequency signals employed by the telemetry system from the lower frequency signals employed by the stimulation or sensing circuitry within the device. The diplexer may include a first filter bank located within the device housing and a second filter bank located external to the device housing. In some embodiments of the invention, the inherent characteristics of the antenna and/or stimulation /sensing lead coupled to the feedthrough may serve to provide some of the required filtering.